Method and appartus for retaining a tool in a tool holder with defined contact surfaces

ABSTRACT

A plurality of friction rods each of which is positioned in a hole around the retaining bore with a portion of each of the plurality of friction rods partially protruding into the retaining bore for directly engaging the shank of the tool for holding the shank of the tool in the retaining bore at the defined contact surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 17/716,591filed Apr. 8, 2022 which application claims the benefit of United StatesProvisional Patent Application No. 63/187,518 filed May 12, 2021, bothof which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to a shrink-fit tool holder, and morespecifically, this disclosure relates to a method and apparatus forretaining a tool in a shrink-fit tool holder by defined contact surfacesaround the circumference of the bore of the tool holder to mechanicallylock the tool to the tool holder.

BACKGROUND INFORMATION

A machining center is a computer numerical control (CNC) machining toolwith an automatic tool-changing function. The machining center canautomatically perform various working such as milling, drilling ornotching, boring, tapping, etc. on works set thereto with improvedefficiency. A tool holder comprises generally of a tapered portionadapted to be connected to a spindle of a machining center, amanipulator-engaging portion, and a tool holding section for firmlyholding the tool.

One type of tool holder is a shrink-fit tool holder, which can firmlyhold a tool with excellent dynamic balancing suitable for high-speedwork. The shrink-fit tool holder comprises of a tapered connectingportion, a manipulator-engaging portion, and a tool holding section forfirmly holding a tool. A shank of the tool is inserted into an apertureof the tool holding section and secured by shrinkage fitting.

The conventional shrink-fit tool holders utilize differences in thermalexpansion coefficients between the tool-holding sections and the toolshanks. The tool shanks are made of materials having low thermalexpansion coefficients such as sintered carbides, high speed steel,etc., while the tool-holding sections are made of high-expansionmaterials such as hot work tool steel, nickel-chromium steel, etc.

In these prior art tool holders, the tool shank and the aperture of thetool-holding sections have suitably controlled sizes to achievedetachability, thereby minimizing the heating for shrinkage fitting andthus preventing decrease in strength and hardness of materials due tochange in their structures. However, in the conventional shrinkage-fittool holders, the difference in a thermal expansion coefficient betweenthe tool-holding member and the tool shank is insufficient, therebycreating opportunities for a failure to achieve a sufficient grippingstrength or a failure to extract the tool.

Accordingly, there is a need for a method and apparatus for retaining atool in a shrink-fit tool holder.

SUMMARY

Disclosed is a tool holder comprising: a first section adapted to beconnected to a machining center; a tool holding section for receivingand holding a shank of a tool therein, wherein the tool holding sectioncomprises of a solid body with an axis of rotation extending therethrough; an outer diameter surface around the solid body; a front faceperpendicular to the axis of rotation; a retaining bore centered on theaxis of rotation and extending from the front face into the solid bodyfor receiving and holding the shank of the tool therein; and a pluralityof friction rods each of which is positioned in a hole around theretaining bore with a portion of each of the plurality of friction rodspartially protruding into the retaining bore for directly engaging theshank of the tool for holding the shank of the tool in the retainingbore at the defined contact surfaces.

In an embodiment, the hole around the retaining bore for receiving thefriction rod is formed in the front face of the solid body and extendsinto the solid body parallel to the axis of rotation, and into which thefriction rod of the plurality of friction rods is fixed.

In another embodiment, the plurality of friction rods are replaced witha plurality of defined contact surfaces. The defined contact surfacescan be formed integral with and as a single piece of material with thesolid body. The plurality of defined contact surfaces can each partiallyprotrude in the retaining bore for directly engaging the shank of thetool for holding the shank of the tool in the retaining bore at thedefined contact surfaces. In such an implementation, a plurality ofdepressions can be formed in the face of the solid body oriented aroundthe bore and comprising between two depressions one of the plurality ofdefined contact surfaces for directly engaging the shank of the tool forholding the shank of the tool in the retaining bore at the definedcontact surfaces.

In another embodiment, a method for creating a shrink-fit tool holderfor retaining a shank of a tool is disclosed. The method can comprise offorming in a front face of a tool holding section centered on arotational axis a retaining bore for holding the shank of the tool; andforming in the front face of the tool holding section of the shrink-fittool holder a plurality of defined contact surfaces each partiallyprotruding in the retaining bore for directly engaging the shank of thetool for holding the shank of the tool in the retaining bore at thedefined contact surfaces.

In an embodiment, the method comprises of forming a plurality ofcircumferentially spaced holes around the retaining bore each forreceiving a friction rod of a plurality of friction rods. The relativediameter of the plurality of circumferentially spaced holes and thefriction rods can be changed, so that the plurality of friction rods canbe placed into the corresponding plurality of circumferentially spacedholes. Thereafter, the method continues with fixing the plurality offriction rods in the corresponding plurality of circumferentially spacedholes by allowing a relative diameter of the circumferentially spacedholes and the plurality of friction rods to equalize. The methodcontinues with fixing the shank of the tool into the retaining bore bychanging a relative diameter of the shank of the tool and the retainingbore.

In another embodiment, the method comprises of forming a plurality ofdepressions around the retaining bore wherein one of the plurality ofdefined contact surfaces is formed between a pair of plurality ofdepressions such that the plurality of defined contact surfaces areformed integral with and as a single piece of material with the toolholding section. The plurality of defined contact surfaces can eachpartially protrude into the retaining bore for directly engaging theshank of the tool for holding the shank of the tool in the retainingbore at the defined contact surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reading the following detailed description, takentogether with the drawings wherein:

FIG. 1 is a partial cross-sectional side view of a tool holder with ashrink-fit bore according to the prior art.

FIG. 2A is a top view of a tool holder with a shrink-fit bore showingthe face of the tool holder drilled with a plurality ofcircumferentially placed holes around the bore.

FIG. 2B is a top view of the tool holder of FIG. 2A with friction rodsinserted into the circumferentially placed holes and the tool holderheated for insertion or extraction of a tool.

FIG. 3 is a top view of the tool holder of FIG. 2B with a tool in thetool holder.

FIG. 4 is a top view of a tool holder according to anotherimplementation.

DETAILED DESCRIPTION

Referring to FIG. 1 , disclosed is a tool holder 100 with a retainingbore 102 that extends from a front face 114 into a solid body 109, whichcan be shrink-fit onto a tool according to the prior art. Tool holder100 comprises of a first section 103 adapted to be connected to amachining center (CNC). This first section 103 can include a taperedconnecting portion 104 configured to be received by a CNC machine (notshown) and a manipulator-engaging portion 106 is designed to be engagedby a clamping system in the CNC machine to hold firmly tool holder 100to the CNC machine spindle. A tool holding section 108 can firmly hold atool 110 (shown in FIG. 3 ) to the tool holder 100. A shank of the toolis inserted into retaining bore 102 of tool holding section 108 andsecured by shrink fitting.

This disclosure is directed to providing a consistent and even pressureto the shank of the tool 110. The grip of the tool holder 100 isimproved by providing in retaining bore 102 of tool holding section 108a plurality of circumferentially placed defined contact surfaces 111 toprovide a mechanical lock of the shank of tool 110. These definedcontact surfaces 111 protrude into retaining bore 102 and directlycontact and hold tool 110. While any number of defined contact surfaces111 could be provided, it is preferable to have three defined contactsurfaces 111 protruding into retaining bore 102 to engage tool 110.Three defined contact surfaces 111 creates a triangle of anchor pointsthat will define the position of tool 110, no matter the shape or otherimperfections in retaining bore 102 or the shape or imperfections of theshank of tool 110. Each retaining bore is different and each tool isdifferent. This arrangement of defined contact surfaces 111 protrudinginto retaining bore 102 ensures that the holding pressure on the shankof tool 110 will always be balanced and there will be zero or near zerorunout (i.e., rotation of the tool off the axis of rotation of the toolholder.

Defined contact surfaces 111 can be formed in retaining bore 102 so thatdefined contact surfaces 111 are integral with the surface of retainingbore 102. Alternatively, defined contact surface 111 can form the outersurface of a friction rod 112 which are placed in corresponding holes113 that are formed in front face 114 of tool holding section 108. Ineither embodiment, defined contact surfaces 111 directly engage theshank of tool 110 to apply consistent and even pressure on tool 110 toprevent runout.

In the embodiment with friction rods 112 and with reference of FIG. 2A,a plurality of circumferentially placed holes 113 are drilled in intofront face 114 of tool holding section 108 around retaining bore 102 oftool holder 100. Thereafter, either tool holding section 108 is heatedto a temperature sufficient to increase the diameter of holes 113 inorder for each of holes 113 to receive a corresponding friction rod 112and/or friction rods 112 are cooled to decrease their diameter. Once therelative temperature between tool holding section 108 and friction rods112 returns to ambient temperature, as shown in FIG. 2B, retaining bore102 has defined contact surfaces 111 corresponding to the location offriction rod 112, which reduces the apparent bore diameter. When tool110 is inserted into retaining bore 102 (typically by reheating toolholding section 108) and tool holding section 108 returns to its ambienttemperature, defined co tact surfaces 111 from friction rods 112 pressagainst tool 110 to lock it in place, as shown it FIG. 3 .

Friction rods 112 are circumferentially spaced around retaining bore 102to keep the center of mass for the rotating tool holder 100 along itsaxis that extends through the center of retaining bore 102. While it ispossible to have unequal distribution of friction rods 112 aroundretaining bore 102, wobbling will occur unless the weight of frictionrods 112 are offset with additional weights. For this reason, three (3)friction rods 112 circumferentially placed one-hundred and twentydegrees (120°) apart may be an optimal distribution of friction rods112; however, any number of a plurality of friction rods 112 can beplaced in tool holding section 108; for example 2, 3, 4, 5, 6, 8, etc.Increasing the number of friction rods 112 beyond 3 does not increasethe usable bore diameter. Rather, it only provides more points ofcontact between defined contact surfaces 111 and the tool 110.

Friction rods 112 can be any diameter depending on the size of toolholding section 108 or retaining bore 102 of tool holder 100. Thediameter of friction rods 112 should be small enough so thatcorresponding hole 113 when placed around retaining bore 102 does notstructurally degrade tool holding section 108. This can occur, forexample, if the distance between friction rod 112 and the outer diameterof tool holding section 108 is too small. Friction rods 112 can eachcomprise two or more friction rods 112 stacked on top of each other,instead of a single long friction rod 112.

Friction rods 112 can be inserted into tool holding section 108 of toolholder 100 in a number of different manners. The goal is to change therelative diameter of friction rods 112 to holes 113 in front face 114 oftool holding section 108. This can be done, for example, by extremecooling of friction rods 112 (for example by immersion in dry ice) or byextreme heating of tool holding section 108. Friction rods 112 can alsobe embedded into holes 113 with extreme force by pressing friction rods112 into holes 111

FIG. 3 shows tool holder 100 with a tool 110 mechanically locked inretaining bore 102 of tool holding section 108. As shown, friction rods112 create corresponding defined contact surfaces 111 on the surface ofretaining bore 102. These defined contact surfaces 111 are the point ofcontact on the shank of tool 110. In fact, a space 116 remains betweenthe side wall of retaining bore 102 and the shank of tool 110. Thebenefits of space 116 will be discussed below.

One skilled in the art will know that with respect to shrink fit toolholders high speed steel (H13) or a high chromium alloy tool steel(SKD61) is the most common metal used for production, although stainlesssteel is also commonly used. Shrink fit tool holders made from anymetals with similar characteristics, however, will benefit from theaddition of friction rods 112 fixed into tool holding section 108.

It may be advantageous to provide friction rods 112 of a dissimilarmaterial. Friction rods can comprise a cemented carbide material, aceramic material, or a hardened steel material. In such instances, asdescribed above, solid body 109 of tool holding section 108 may compriseH13, SKD61, or stainless steel. For the purpose of this disclosure,friction rods 112 can comprise any material.

Another advantage is that a portion of material in tool holding section108 is removed from forming holes 113. This less material means thatless heat is required to insert and remove tools 110 from tool holdingsection 108. Similarly, tool holding section 108 will cool faster.

In another embodiment, as shown in FIG. 4 , defined contact surfaces 111can be formed by machining a small portion 121 of retaining bore 102away in three positions each one hundred and twenty degrees (120°)apart. The depth of this machining can be very small (<0.0005″) or largeenough extending the depth of bore 102 for coolant to pass through. Thedepth can also be any depth between this range. This will not make bore102 more rigid or impact the vibration like adding friction rods 112,and may also be much cheaper and easier to integrate into tool holder100. While three small portions 121 are disclosed any number of smallportions 121 are contemplated. What is left when small portions 121 areremoved, is bore 102 centered on the rotational axis, as in theembodiments discussed above, with three defined contact surfaces 111extending to the outer-diameter of bore 108 to engage the shank of thetool.

It should also be noted that when tool 110 is difficult to extract fromretaining bore 102, operators tend to overheat tool holder 100 to try toincrease the expansion of retaining bore 102. This can cause permanentdamage to tool holder 100. Friction rods 112 will reduce the number oftool holders damaged by overheating, by providing improvedextractability.

If the height of defined contact surfaces 111 is kept very small nocoolant will flow around the tool and coolant holes can be added as withany shrink fit tool holder. Increasing the height of defined contactsurfaces 111, however, will allow coolant to flow along tool 110. Thiscan provide enhanced cooling of tool 110.

A method for creating a tool holder 100 is also disclosed. The methodbegins at step 202 and proceeds to step 204 by forming in front face 114of tool holding section 108 a plurality of circumferentially spacedholes 113 around an axis of rotation of tool holding section 108. Nextretaining bore 102 is formed with its center on the axis of rotation.This create a surface of retaining bore 102 that is discontinuous forreceiving friction rods 112. At step 206 the relative diameter of holes113 to friction rods 112 is temporarily changed. This can occur byheating of tool holding section 408 or cooling friction rods 112. Themethod continues at step 208 by inserting friction rods 112 into holes113. The method continues at step 210 by fixing friction rods 112 incorresponding holes 113 by allowing the relative diameter of holes 113to friction rods 112 to return to normal. This creates defined contactsurfaces 111 that protrude in retaining bore 102 that can directlyengage the shank of tool 110.

The method can continue at step 212 by inserting shank of tool 110 intothe retaining bore. At step 214 tool holder is allowed to cool andreturn to its ambient state with a smaller diameter retaining bore 102and with defined contact surfaces 111 mechanically locking tool 110 intoretaining bore 102. Step 212 can be repeated when it comes time toremove tool 110 from retaining bore 102.

While the principles of the invention have been described herein, it isto be understood by those skilled in the art that this description ismade only by way of example and not as a limitation as to the scope ofthe invention. Other embodiments are contemplated within the scope ofthe present invention in addition to the exemplary embodiments shown anddescribed herein. Modifications and substitutions by one of ordinaryskill in the art are considered to be within the scope of the presentinvention, which is not to be limited except by the following claims.

1-10. (canceled)
 11. A method for creating a shrink-fit tool holder forretaining a shank of a tool, the method comprising: forming in a frontface of a tool holding section centered on a rotational axis a retainingbore for holding the shank of the tool; and forming in the front face ofthe tool holding section of the shrink-fit tool holder a plurality ofdefined contact surfaces each partially protruding in the retaining borefor directly engaging the shank of the tool for holding the shank of thetool in the retaining bore at the defined contact surfaces.
 12. Themethod for creating the shrink-fit tool holder of claim 11, furthercomprising forming a plurality of circumferentially spaced holes aroundthe retaining bore each for receiving a friction rod of a plurality offriction rods.
 13. The method for creating the shrink-fit tool holder ofclaim 12, further comprising changing a relative diameter of theplurality of circumferentially spaced holes and the friction rods. 14.The method for creating the shrink-fit tool holder of claim 13, furthercomprising inserting the plurality of friction rods into thecorresponding plurality of circumferentially spaced holes.
 15. Themethod for creating the shrink-fit tool holder of claim 14, furthercomprising fixing the plurality of friction rods in the correspondingplurality of circumferentially spaced holes by allowing a relativediameter of the circumferentially spaced holes and the plurality offriction rods to equalize.
 16. The method for creating the shrink-fittool holder of claim 15, further comprising inserting the shank of thetool into the retaining bore.
 17. The method for creating the shrink-fittool holder of claim 16, wherein the step of inserting the shank of thetool into the retaining bore further comprises changing a relativediameter of the shank of the tool and the retaining bore.
 18. The methodfor creating the shrink-fit tool holder of claim 11, further comprisingforming a plurality of depressions around the retaining bore wherein oneof the plurality of defined contact surfaces is formed between a pair ofplurality of depressions such that the plurality of defined contactsurfaces are formed integral with and as a single piece of material withthe tool holding section, and wherein the plurality of defined contactsurfaces each partially protrude into the retaining bore for directlyengaging the shank of the tool for holding the shank of the tool in theretaining bore at the defined contact surfaces. 19-20. (canceled) 21.The method for creating the shrink-fit tool holder of claim 11, whereinthe defined contact surfaces are each fixed to and partially protrudinginto the retaining bore.
 22. The method for creating the shrink-fit toolholder of claim 11, wherein the defined contact surfaces each have ahardness greater than or equal to the solid body.
 23. The method forcreating the shrink-fit tool holder of claim 11, wherein the definedcontact surfaces extend from the front face and downward parallel withthe retaining bore.
 24. A method for creating a shrink-fit tool holderfor retaining a shank of a tool, the method comprising: forming in afront face of a tool holding section centered on a rotational axis aretaining bore for holding the shank of the tool; and forming aplurality of depressions around the retaining bore with defined contactsurfaces between pairs of depressions of the plurality of depressionssuch that the defined contact surfaces are formed integral with and as asingle piece of material with the tool holding section, and wherein thedefined contact surfaces partially protrudes into the retaining bore fordirectly engaging the shank of the tool for holding the shank of thetool in the retaining bore at the defined contact surfaces.
 25. Themethod for creating the shrink-fit tool holder of claim 24, wherein thedefined contact surfaces are each fixed to and partially protruding intothe retaining bore.
 26. The method for creating the shrink-fit toolholder of claim 24, wherein the defined contact surfaces each have ahardness greater than or equal to the solid body.
 27. The method forcreating the shrink-fit tool holder of claim 24, wherein the definedcontact surfaces extend from the front face and downward parallel withthe retaining bore.
 28. The method for creating the shrink-fit toolholder of claim 24, wherein the defined contact surfaces extend from thefront face and downward parallel with the retaining bore and each havinga hardness equal to the solid body and fixed to and partially protrudinginto the retaining bore for directly engaging the shank of the tool andfor holding the shank of the tool in the retaining bore at the definedcontact surfaces.